get_categories for Custom Post Type

1 Views

I have a Custom Post Type, ‘ioni_codex’
I am using built-in WordPress category as taxonomy

I want to list all categories used by ‘ioni_codex’.

Read More

I assume that this code will do the trick: 

$myargs = array (
    'type' => 'ioni_codex'
); 
$categories = get_categories( $myargs );

However instead I see the list of all categories not the categories assigned to by ‘ioni_codex’.

What Am I doing wrong?

Post Views: 1

Related posts

Leave a Reply

4 comments

  2. Instead of type you have to set post_type , by default get_categories try to hide empty categories , if you want display it all add hide_empty property set to false 

     get_categories(array(
    'post_type' => 'ioni_codex',
    'hide_empty' => false,
   ) );

  3. I have an answer at a sister project:
    Bainternet♦ has re-written get_terms() function to provide for the post_type

    Please refer to his solution here or just copy and past from below:

    /* get terms limited to post type 
 @ $taxonomies - (string|array) (required) The taxonomies to retrieve terms from. 
 @ $args  -  (string|array) all Possible Arguments of get_terms http://codex.wordpress.org/Function_Reference/get_terms
 @ $post_type - (string|array) of post types to limit the terms to
 @ $fields - (string) What to return (default all) accepts ID,name,all,get_terms. 
 if you want to use get_terms arguments then $fields must be set to 'get_terms'
*/
function get_terms_by_post_type($taxonomies,$args,$post_type,$fields = 'all'){
    $args = array(
        'post_type' => (array)$post_type,
        'posts_per_page' => -1
    );
    $the_query = new WP_Query( $args );
    $terms = array();
    while ($the_query->have_posts()){
        $the_query->the_post();
        $curent_terms = wp_get_object_terms( $post->ID, $taxonomy);
        foreach ($curent_terms as $t){
          //avoid duplicates
            if (!in_array($t,$terms)){
                $terms[] = $c;
            }
        }
    }
    wp_reset_query();
    //return array of term objects
    if ($fields == "all")
        return $terms;
    //return array of term ID's
    if ($fields == "ID"){
        foreach ($terms as $t){
            $re[] = $t->term_id;
        }
        return $re;
    }
    //return array of term names
    if ($fields == "name"){
        foreach ($terms as $t){
            $re[] = $t->name;
        }
        return $re;
    }
    // get terms with get_terms arguments
    if ($fields == "get_terms"){
        $terms2 = get_terms( $taxonomies, $args );
        foreach ($terms as $t){
            if (in_array($t,$terms2)){
                $re[] = $t;
            }
        }
        return $re;
    }
}

  4. While quick reading @ioni’s answer; it looks like it would give you a proper result it will most likely be pretty slow as it goes through every post and then looks for all terms that belong to each post individually. This will easily result in thousands of SQL queries.

    My recommendation is to use a single query to get the IDs of all terms that belong to a post type. Then use those ids to filter get_terms().

    MySQL query:

    SELECT
    wp_term_taxonomy.term_id
FROM
    wp_term_relationships
LEFT JOIN wp_posts ON wp_term_relationships.object_id = wp_posts.ID
LEFT JOIN wp_term_taxonomy ON wp_term_relationships.term_taxonomy_id = wp_term_taxonomy.term_taxonomy_id
WHERE
    wp_term_taxonomy.taxonomy = 'category'
AND wp_posts.post_type = 'ioni_codex'
GROUP BY
    term_id

    PHP function:

    <?php

function ioni_get_terms_by_post_type( $taxonomy = 'category', $post_type = 'post', $args = array() ) {
    global $wpdb;

    $sql = $wpdb->prepare(
        "
            SELECT
                {$wpdb->prefix}term_taxonomy.term_id
            FROM
                {$wpdb->prefix}term_relationships
            LEFT JOIN {$wpdb->prefix}posts ON {$wpdb->prefix}term_relationships.object_id = {$wpdb->prefix}posts.ID
            LEFT JOIN {$wpdb->prefix}term_taxonomy ON {$wpdb->prefix}term_relationships.term_taxonomy_id = {$wpdb->prefix}term_taxonomy.term_taxonomy_id
            WHERE
                {$wpdb->prefix}term_taxonomy.taxonomy = '%s'
            AND {$wpdb->prefix}posts.post_type = '%s'
            GROUP BY
                term_id
        ",
        $taxonomy,
        $post_type,
    );
    $term_ids = $wpdb->get_col( $sql );
    
    if ( empty( $term_ids ) ) {
        return array();
    }

    // custom code to allow for exclude to work
    if ( ! empty( $args['exclude'] ) ) {
        // allow exclude to be either a string or array
        $exclude = is_string(  $args['exclude'] ) ? (array) $args['exclude'] : $args['exclude'];
        
        // filter $term_ids with array from $args['exclude']
        $term_ids = array_filter( $term_ids, function( $term_id ) use ( $exclude ) {
            return ! in_array( $term_id, $exclude );
        } );
    }

    $args = wp_parse_args(
        $args,
        array(
            'taxonomy' => $taxonomy,
            'include' => $term_ids,
        ),
    );

    return get_terms( $args );
}

    Usage:

    <?php

$categories = ioni_get_terms_by_post_type( 'category', 'ioni_codex' );